Rising damp

Rising damp occurs when ground water soaks into a wall which then migrates steadily upwards. Worried house owners often notice damp stained walls or deterioration of the internal decorations and plasterwork.

The distinct water stains on the base of this wall is a well recognised characteristic of rising damp. The plaster has been extended down and rests on a concrete floor, which can bridge the damp proof course. Had the builders left a small gap between the plasterwork and the floor, our services would not have been needed.

Again, this picture shows the typical signs of rising damp. The top edge of the stain is the maximum height to which the damp has risen and is where the highest concentration of hygroscopic salts is found.

The staining on this wall is accompanied by deposits of efflorescent salts.

Externally, rising damp can be recognised through distinct staining visible on the base of ground floor walls, and deterioration of the masonry is common. Staining is often caused through contamination of the masonry with hygroscopic salts. These salts, by absorbing moisture from the air, cause the contaminated material to exhibit significant dampness even after the original moisture source has been rectified. This is the prime reason why internal plaster is usually replaced when a remedial damp proof course is installed.

Staining at the base of this wall clearly indicates the height to which the dampness has risen. In this specific case, higher than one metre. The thriving collection of weeds at the base of this wall suggests that this location is very damp.

Dampness on this wall is accompanied by deposits of efflorescence, which look like white, fluffy salt.

The base of this wall has been rendered. Render is often applied as a remedy for perished brick or stonework. Unfortunately, the render can inhibit evaporation which can drive moisture further up the wall causing damage to the masonry above, as seen in this image.

The height to which rising damp can climb is dependent on a number of factors that include the nature of the masonry, the rate of evaporation, and the thickness of the walls. Theoretically, damp can rise many metres, but, in practice, it is usually restricted to the base of walls, no higher than one metre.

Rising damp on this wall extends to a height in excess of 2.0m. The wall has been repointed, but hygroscopic salts have discoloured the new mortar so it appears distinctly darker than wall above.

The problems with this house are two fold:

1) The brickwork on the front wall of this house is clearly affected by rising damp. A distinct band has been created that extends from the ground floor window sill to the top of the door head. This band results from seasonal movement of moisture depositing hygroscopic salts.

2) The rainwater fall pipe is damaged, allowing water to discharge onto the brickwork at first floor level. This has created a roughly circular stain that has characteristic white efflorescent salts around the perimeter.

On this stone wall, rising damp extends to a height of around 2.0m. The dampness reached the same height on the internal side of this wall.

True rising damp occurs because there is no effective means of preventing the movement of moisture in the ground up the wall. Often, this is because the wall has not been protected with an effective damp proof course. However, rising damp is technically a description of a process and is not a source of moisture. In fact, any source of moisture affecting the base of a wall can cause similar symptoms. The important point made here is that 'rising damp' is not necessarily a result of a missing or defective damp proof course and may not require the installation of a new damp proof course.

The base of this wall is obviously damp. The root cause of the problem was the plaster extending down onto a solid floor. This bridged the damp proof course and allowed damp to take hold. The remedy was simple and practical. The plaster was trimmed back and the floor/wall junction was sealed.

This wall is showing signs of damp because the floor on the other side of the wall is at a higher level and is solid, which allows the damp to penetrate the wall.

The base of this wall appears to be very damp, but the reading on this moisture meter shows 16%, which is quite dry. The staining was actually caused by oil and not moisture.

Britannia Preservation's surveyors carry out a careful assessment of the property. Initially using non-invasive methods, but laboratory analysis, carbide meter tests, salts analysis, thermal imaging, and other techniques may be recommended to establish the precise cause.

Where it is considered necessary to install a damp proof course, Britannia Preservation employs several different remedial methods. These include physical damp proof courses, damp proofing creams, and electro-osmosis.

Rising damp is not necessarily the result of a missing damp proof course. Instead, it can be caused by other defects including bridging, plumbing leaks, rainwater penetration, condensation, and other factors. Rectification of these defects does not require the installation of a damp proof course. Furthermore, in some circumstances such as the case with period property, and particularly listed buildings, it may not be appropriate or permissible to utilise contemporary damp proof course methods. That is not to say that dampness cannot be alleviated or managed, only that due consideration should be given to causation and the context of the remedy.

Unfortunately, there can be a presumption that dampness affecting the base of a wall is a result of a failed damp proof course. This presumption often results in unnecessary, costly, disruptive, and inappropriate remedial works being carried out. Fortunately, Britannia Preservation's investigation methods mean that this situation is avoided. Only after the true cause of dampness has been established and all significant factors have been taken into account, will we confirm the appropriate remedies and draw up a plan of action for you.